The pervasive use of fossil fuels as the primary energy source for most transportation, space heating and industrial activity has led to the release of increasingly large of amounts of carbon dioxide (CO2) into the atmosphere. The resulting increase in CO2 concentration in the atmosphere is believed by the climate research community to be a primary driver of global warming. Because of the potentially dire economic and human consequences of global warming, extensive efforts are being made to reduce all Green House Gas Emissions including CO2 and CH4 from dump sites and landfills wherever possible.
In view of the large fraction of the global economy that runs on gas and liquid hydrocarbon fuels (currently derived almost exclusively from fossil fuels), alternative fuels that can serve as replacements with a minimum of technological adjustment are desirable. Additionally, there is substantial demand for other fossil fuel-based feedstocks from the chemical industry. Therefore, there is a need for gas and liquid fuels, as well as other chemical feedstocks, the production and/or use of which results in reduced CO2 emissions as compared to use of the fossil fuel equivalents. Carbon dioxide emissions from fossil fuel can be reduced by using pyrolysis of biomass and other waste streams to produce alternative fuels and feedstocks.
The world generated 1.4 trillion tonnes of municipal solid waste (MSW) in 2014. Of that total, 43% was landfilled, 9% was disposed in dump sites, 16% was incinerated, 9% was composted, and only 17% is recycled (What a Waste: A Global Review of Solid Waste Management, World Bank). The percentage of waste sent to the landfill and dumped could be reduced to less than 26%, using integrated materials and energy recovery. Mixed MSW may be sorted with the use of mechanical and optical technologies to extract (i) recyclables (plastic bottles, cardboard, paper, metals and glass/ceramics) and (ii) wet organic waste (food and yard waste) for anaerobic digestion to produce bio-gas, and (iii) compost and residual mixed unrecyclable waste (film plastics, plastic cups/plates, dirty unrecyclable paper/cardboard, diapers, and wood chips) for pyrolysis to produce biofuels.
MSW is not the only source of biomass for biofuel production. Materials such as wood wastes from forestry operations, crop residues from agriculture, and animal wastes may be used. Because biomass of these types ultimately are derived from photosynthesis, combustion of its derivatives does not add new CO2 to the atmosphere, thereby resulting in a concomitant reduction in CO2 emissions.
Pyrolysis is one of a number of processes that can be used to convert biomass and other sources of hydrocarbon-containing materials into gas and liquid fuels and other chemical feedstocks. Pyrolysis is a chemical process whereby hydrocarbon-containing materials can be thermally decomposed in the absence of free oxygen, and whereby useful hydrocarbon liquids, gases and other materials are produced as a result of that thermal decomposition from the biomass or other starting material. The products of pyrolysis can be further processed to produce gas and liquid fuels and other feedstocks required by the chemical industry.
While the chemical principles of pyrolysis have been well understood for several decades, it has only recently been applied to large-scale conversion of biomass and other hydrocarbon-containing waste streams. While many types of reactors are used for conducting pyrolysis, there is a need to provide a pyrolysis reactor with more efficient feedstock conversion in pyrolysis. One of the biggest challenges for commercial-scale pyrolysis is the reliability of continuous processing. Maintaining an oxygen free environment is critical to pyrolysis and has been very difficult to achieve. In one embodiment, the present invention provides a batch reactor that functions in a semi-continuous mode and provides sufficient throughput per reactor volume to satisfy the commercial scale requirement.